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Galapagos islands, evolution and sea levels

This movie is a simple 0 m to -210 m geographical loop sequence at 5 m increments. Important features are the substantial gaps between Galapagos’ “core” islands even at -100 m. However, below c. -130 m the various islands begin coalescing.

Writing in the Journal of Biogeography, Jason Ali and Jonathan Aitchison explore how fluctuating sea level changes over thousands of years impacted the island chain’s ecology. They estimate that when the sea retreated, most recently 20,000 years ago, the water would have been 144m below its current level.

As a result, Santa Cruz, the island in the center of the archipelago, would have expanded, enveloping many of the smaller islands, while creating a series of shallow ‘land bridges’ between the volcanic outcroppings. Such bridges explain the range and diversity of the islands’ species, such as snakes, geckos and iguanas, which appear landlocked to modern eyes.

“As soon as I saw that that half the islands in the archipelago were sat on a single, shallow, submarine platform, I realized that the implications for biology could be significant,” said Dr. Ali. “My geological knowledge told me that sea-level falls must have regularly re-connected the islands, and that this must have profoundly shaped the landlocked biota’s distribution, and very likely its composition.”

Ecuador has declared an emergency in the Galapagos Islands, saying that a cargo ship which ran aground last week still poses a threat to the archipelago’s fragile ecosystem: here. See also here.